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The sensitivity of the CERN FCC-ee collider to the production of heavy neutral leptons (HNL) is investigated. The study focuses on a simplified model with a single low-mass HNL mixing with a muon, and addresses the fully leptonic and semileptonic decay modes of the HNL. Complete Monte Carlo analyses of signal and background based on a parametrised detector simulation are performed for the FCC-ee run at the Z pole, resulting in an estimate of the intervals of the mixing parameter for which the FCC-ee will have a 95% CL sensitivity as a function of the HNL mass.

This report presents an overview of some of the most recent results obtained by the ATLAS Collaboration using pp and heavy-ion collisions at the LHC. The review is not intended to be comprehensive and includes recent updates on the Higgs boson properties, precision Standard Model measurements, as well as searches for new physics. Most of the results exploit the data collected in the last LHC run, providing pp collisions at a centre of mass energy of 13 TeV.

We investigate possible signatures of long-lived (or stable) charged black holes at the Large Hadron Collider. In particular, we find that black hole remnants are characterised by quite low speed. Due to this fact, the charged remnants could, in some cases, be very clearly distinguished from the background events, exploiting dE / dX measurements. We also compare the estimate energy released by such remnants with that of typical Standard Model particles, using the Bethe–Bloch formula.

We investigate possible signatures of black hole events at the LHC in the hypothesis that such objects will not evaporate completely, but leave a stable remnant. For the purpose of defining a reference scenario, we have employed the publicly available Monte Carlo generator CHARYBDIS2, in which the remnant’s behavior is mostly determined by kinematic constraints and conservation of some quantum numbers, such as the baryon number. Our findings show that electrically neutral remnants are highly favored and a significantly larger amount of missing transverse momentum is to be expected with respect to the case of complete decay.

The multi-staged XENON program at INFN Laboratori Nazionali del Gran Sasso aims to detect dark matter with two-phase liquid xenon time projection chambers of increasing size and sensitivity. The XENONnT experiment is the latest detector in the program, planned to be an upgrade of its predecessor XENON1T. It features an active target of 5.9 tonnes of cryogenic liquid xenon (8.5 tonnes total mass in cryostat). The experiment is expected to extend the sensitivity to WIMP dark matter by more than an order of magnitude compared to XENON1T, thanks to the larger active mass and the significantly reduced background, improved by novel systems such as a radon removal plant and a neutron veto. This article describes the XENONnT experiment and its sub-systems in detail and reports on the detector performance during the first science run.

Xenon dual-phase time projection chambers designed to search for weakly interacting massive particles have so far shown a relative energy resolution which degrades with energy above ∼ 200 keV due to the saturation effects. This has limited their sensitivity in the search for rare events like the neutrinoless double-beta decay of 136 Xe at its Q value, Q β β ≃ 2.46 MeV . For the XENON1T dual-phase time projection chamber, we demonstrate that the relative energy resolution at 1 σ / μ is as low as ( 0.80 ± 0.02 ) % in its one-ton fiducial mass, and for single-site interactions at Q β β . We also present a new signal correction method to rectify the saturation effects of the signal readout system, resulting in more accurate position reconstruction and indirectly improving the energy resolution. The very good result achieved in XENON1T opens up new windows for the xenon dual-phase dark matter detectors to simultaneously search for other rare events.

The selection of low-radioactive construction materials is of the utmost importance for rare-event searches and thus critical to the XENONnT experiment. Results of an extensive radioassay program are reported, in which material samples have been screened with gamma-ray spectroscopy, mass spectrometry, and 222Rn emanation measurements. Furthermore, the cleanliness procedures applied to remove or mitigate surface contamination of detector materials are described. Screening results, used as inputs for a XENONnT Monte Carlo simulation, predict a reduction of materials background (∼17%) with respect to its predecessor XENON1T. Through radon emanation measurements, the expected 222Rn activity concentration in XENONnT is determined to be 4.2 (-0.7+0.5) μBq/kg, a factor three lower with respect to XENON1T. This radon concentration will be further suppressed by means of the novel radon distillation system.

Measurements of open charm production cross sections in deep-inelastic ep scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections for charm production are obtained in the kinematic range of photon virtuality 2.5≤ Q 2 ≤2000 GeV 2 and Bjorken scaling variable 3⋅10 −5 ≤ x ≤5⋅10 −2 . The combination method accounts for the correlations of the systematic uncertainties among the different data sets. The combined charm data together with the combined inclusive deep-inelastic scattering cross sections from HERA are used as input for a detailed NLO QCD analysis to study the influence of different heavy flavour schemes on the parton distribution functions. The optimal values of the charm mass as a parameter in these different schemes are obtained. The implications on the NLO predictions for W ± and Z production cross sections at the LHC are investigated. Using the fixed flavour number scheme, the running mass of the charm quark is determined.

This report describes the experimental strategy and technologies for XLZD, the next-generation xenon observatory sensitive to dark matter and neutrino physics. In the baseline design, the detector will have an active liquid xenon target of 60 tonnes, which could be increased to 80 tonnes if the market conditions for xenon are favorable. It is based on the mature liquid xenon time projection chamber technology used in current-generation experiments, LZ and XENONnT. The report discusses the baseline design and opportunities for further optimization of the individual detector components. The experiment envisaged here has the capability to explore parameter space for Weakly Interacting Massive Particle (WIMP) dark matter down to the neutrino fog, with a 3 σ evidence potential for WIMP-nucleon cross sections as low as 3 × 10 - 49 c m 2 (at 40 GeV/c 2 WIMP mass). The observatory will also have leading sensitivity to a wide range of alternative dark matter models. It is projected to have a 3 σ observation potential of neutrinoless double beta decay of 136 Xe at a half-life of up to 5.7 × 10 27  years. Additionally, it is sensitive to astrophysical neutrinos from the sun and galactic supernovae.

Radiogenic neutrons emitted by detector materials are one of the most challenging backgrounds for the direct search of dark matter in the form of weakly interacting massive particles (WIMPs). To mitigate this background, the XENONnT experiment is equipped with a novel gadolinium-doped water Cherenkov detector, which encloses the xenon dual-phase time projection chamber (TPC). The neutron veto (NV) can tag neutrons via their capture on gadolinium or hydrogen, which release γ -rays that are subsequently detected as Cherenkov light. In this work, we present the first results of the XENONnT NV when operated with demineralized water only, before the insertion of gadolinium. Its efficiency for detecting neutrons is ( 82 ± 1 ) % , the highest neutron detection efficiency achieved in a water Cherenkov detector. This enables a high efficiency of ( 53 ± 3 ) % for the tagging of WIMP-like neutron signals, inside a tagging time window of 250 μ s between TPC and NV, leading to a livetime loss of 1.6 % during the first science run of XENONnT.